1. In continuing our work on the theoretical description of interfacial reaction dynamics we have reformulated the expression for the diffusion controlled dissociation rate constant such that it is applicable to cases where the dissociating moieties have significantly disparate sizes (e.g., ligand dissociating from a cell surface). Our correction is equivalent to mathematically acknowledging that the reactants have finite sizes and are not mutually interpenetrable. We have also shown analytically the equivalence of the branching method and the classical kinetic formulation for evaluating diffusion controlled reactions. 2. We have continued our development of the theory of interactions between transmembrane proteins and the membrane electric potential. The equations and theory developed allow us to calculate the influence of changes in the electric field on the function of membrane proteins. If the membrane potential is caused to oscillate, or to randomly fluctuate in a manner uncorrelated to the enzyme state in the region of fluctuation, an enzyme can transduce energy from the modulated potential and convert it to stored chemical energy (e.g., ATP synthesis or the formation of an ion gradient). This of great theoretical importance in interpreting experiments in which ATP synthesis is observed even when there is apparently "insufficient" thermodynamic driving force contained in the proton elecrochemical gradient. Considerations along these lines have resulted in the development of a very simple physical model for energy transduction. While this model certainly does not represent an accurate description of any one actual enzyme, its simplicity makes it an outstanding tool for understanding one physical mechanism by which an enzyme could couple two chemical reactions.